Folding Bowsprit

ABSTRACT

The Folding Bowsprit permits deployment of sails from a point forward of the bow on sailing vessels. The folding function allows the sprit to rotate around an axis at ninety degrees to the vessels centerline and permits the end of the sprit to move vertically up or down. This unique ability to fold facilitates:
         compact stowage when not in use and reduces the overall length of the vessel;   adjustment of tack position vertically while sailing;   safer and simpler sail handling by accessing the tack point of said sprit within the deck footprint while sailing.

BACKGROUND

Modern sailboats are re-inventing themselves in the never ending questto become faster, safer and easier to handle. One common trend insailboat design borrows a concept from yesteryear by utilizing a sparmounted on the front (bow) of a boat to extend the tack point (fig m)forward for the attachment of sails, this spar is know as a bowsprit.This phenomenon is partly driven by contemporary designs having morevertical or plumb bows, than the sweeping lines of long overhangstypical in sailing vessels designed in the first half of the 20^(th)century. Modern designs tend to extend the waterline length to theextremities of the bow and the stern (fig m), thus maximizing speedpotential for a certain sized length over all (LOA). The market demandsthe fastest boat possible for a certain length as this dimension drivesthe overall cost of ownership, as monthly storage charges are based onLOA and various other ownership costs tend to be proportional to the LOAcubed.

With the evolution of plumb bows, sailors have forfeited the ability todeploy sails well forward of the mast thereby compromising the sailforward of the mast. A reduction in forward sail-area also impacts thesteering balance of the vessel. The further the tack point (fig m) is infront of the mast the larger is the area of the sail that can bedeployed. Furthermore boat steering and is enhanced and overallperformance improved when the center of effort (which approximates to bethe center of sail area) is well in front of the center of resistance(which approximates to be the center of displacement). This stabilizingconcept is analogous to the vessel being pulled through the water ratherthan pushed and requiring less corrective steering which is detrimentalto speed.

Modern boats are capitalizing on aforementioned beneficialcharacteristic by rediscovering this once forgotten spar, the bowsprit.The challenge therefore becomes how can modern boats capitalize onbenefits of this forward protruding spar without permanently beingeffected by it's encumbrances that escalate storage costs and generalawkwardness.

Currently there are three concepts active in the marketplace attemptingto solve this issue:

-   -   1. Permanent sprit reinforced by a bob-stay (guy that angles        back to the bow of the boat and attaches just above the        waterline.    -   2. Telescoping sprit installed through the bow of the boat.    -   3. Telescoping sprit installed above deck and offset to avoid        essential rigging.

Pros & Cons of aforementioned bowsprit concepts:

Concept 1 simply extends the tack of the sail forward but does nothingto decrease the overall LOA when the boat is in a storage configuration;therefore storage is awkward and expensive. Remaining in a permanentlyprotruded configuration is detrimental to maneuvering the vessel intight quarters, and can be difficult or dangerous to service or adjustwhen the vessel is underway.

Concept 2 helps solve the storage issue by retracting into the vesselsinterior thus reducing the LOA but requires significant structuralupgrading to handle the extremely high point loading configuration. Saidconcept has been integrated into the design of many contemporary boatshowever there is a significant interference with space in the bowinterior. Furthermore this configuration requires a large diameter holefacing directly forward into oncoming seas and leakage around thisopening is common. No serious ocean going vessel would consider suchbreach in the water-tightness of the vessel in this area. Retrofittingthis configuration is expensive and complex due to the structuralupgrade requirements. The loads developed in this cantilevered sprit areintense. From an engineering perspective this cantilevered bending modeis the least efficient means to carry a load as it results in a largersectional requirement to limit deflection to an acceptable level.Consequently these sprits tend to be larger in diameter and heavier inweight than a comparable sprit supported by a bob-stay.

Concept 3 is similar to 2 except it is mounted above the deck and wouldseem to have the best of all worlds. In practice however the deckmounted telescoping spar develops extremely high point loads andrequires significant structural upgrades prior to installation. Withouta bob-stay the loads are carried by cantilever and is subjected to saidissues as illustrated for item 2. This configuration also creates deckclutter as it obstructs the foredeck area of the vessel. Sailing vesseldeck space should remain clear and unfettered to permit the crew safeand easy access. Space at the bow is at an absolute premium and anysmall protrusion of hardware because a serious trip hazard whentraversing this space in any sea condition. Another unfortunate aspectwith this concept is that it is visually unappealing. A sailing boat'sbeauty is defined by it's vessels lines. Aesthetics tend to becompromised whenever appliances are installed at either end of a vesselthat break or obstruct these natural lines. Lastly due to riggingconfigurations the forward stay (head stay) on a sailing vessel isalways mounted on centerline, this is exactly the same location desiredfor a deck mounted retracting bowsprit. The compromise becomes an angledoffset which adds to the overall awkwardness of the look installationand operation of this device. Adjustment or retrieval of any telescopingsprit is next to impossible while in the sailing mode due to the highlateral loading forces. This can result in complications in sailretrieval if accessing the tack point is required and in certainsituations compound into a hazardous event.

Prior Art

Retractable bowsprit for sailboat—U.S. Pat. No. 7,367,276

Sailboat spinnaker bowsprit—U.S. Pat. No. 6,857,380

Folding Bowsprit Description

The Folding Bowsprit is an adaptation of the traditional wooden bowspritand supported by a bob-stay which has been in use on sailing vessels forcenturies. The primary purpose of the bowsprit is to maximize sail areadeployment by extending the tack position further forward of the mastthan as permitted by the constraints of a vessels deck. The secondarypurpose of the sprit is to provide a more balanced sail plan by movingthe center of effort forward which in certain conditions reduce steeringloads and improve overall sailing performance and speed.

The Folding Bowsprit has an elegantly simple yet unique geometry similarin concept to a forward protruding wishbone. Said sprit is pinned to thevessel via a hinge installed just below the deck line near the bow. Theaxis of rotation permits movement from the horizontal position (whensailing) to the vertical position (when adjusting or storage). The angleof rotation is controlled by an adjustable bob stay which facilitatesvertical movement and luff tension (fig m) while in the sailing mode.The sprit's primary function is to extend the tack position of headsailsand spinnakers forward of the bow stem and is effectively horizontalwhen in the sailing configuration. Said sprit does not clutterdeck-space or inhibit crew mobility at the bow area in any way. Saidsprit can be rotated to a vertical position when sailing to facilitateadjustments to the tack of the sail from the safety of the deck area.Crew can reach tack without extension beyond the safety of the lifelinesand associated expose to falling overboard. Furthermore the sprit can berotated to a vertical position which minimizes the LOA and facilitatesmaneuvering in tight spaces or at the dock, thus resulting in a saferboating experience and lower storage costs.

The unique characteristics of the Folding Bowsprit are:

-   -   “Wishbone” configuration of two separate spars joining the hull        just behind the bow at a hinged connection allowing rotation        around an axis at ninety degrees to the vessels centerline and        permits the forward end of the sprit to move vertically up or        down.    -   Instead of a fixed bobstay the said sprit has an adjustable        bob-stay which permits vertical moment of the sprit up and down        which in turn adjusts the luff tension of the attached sail        which is instrumental in achieving correct sail trim in varying        conditions.    -   Instead of one point of attachment as evidenced in telescoping        sprits (and associated high loading due to cantilevering), or a        two point of connection configuration as evidenced in        traditional sprit with bob-stay supported the Folding Bowsprit        is effectively connected at three points (one at each side of        the hull and the third at the bob-stay point of connection.        These three points of attachment evenly distribute loads over a        wide area.

Consequently structural upgrades to a vessels hull are typicallyrequired. Loads within the spar members are carried 100% in compression,which is the most efficient means of transferring loads. This permitssmaller sections which are lighter and have less windage. Smallersections have more subtle visual impact than massive apparatus in otherconfigurations.

DESCRIPTION OF DRAWINGS

There are four (4) sheets of drawings included with this applicationwhich describe the geometry, assembly and application on a typicalsailboat.

Drawing 001

fig a—is a top view elevation of a typical sailboat indicating theFolding Sprit within the detail B.

fig b—is an enlargement of a top view of said sprit, indicating thewishbone configuration and attachment point near the bow of the boat.

fig c—is an enlargement of detail A illustrating the adjustable bob staygeometry.

fig d—is a side view of a typical sailboat indicating the said spritwithin detail A.

fig e—is an isometric view of a typical sailboat and indicates thefollowing key parts of the boat, Bow, Deck, Stern and Mast.

Drawing 002

fig f—is the top view of a typical sailboat and illustrates up positionof the said Sprit in Detail C.

fig g—is the enlargement of detail C with said sprit in up position.

fig h—is the enlargement of detail E of said sprit in up position.

fig i—is the side view of a typical sailboat with sail sprit in upposition per detail E.

fig j—is an isometric view of detail D

fig k—is an isometric view of a typical sailboat with said sprit in upposition per detail D.

Drawing 003

fig l—is a side view indicating the up and down movement around thehinge.

fig m—is a side view of a typical sailboat utilizing said sprit todeploy sail, location of sail tack, and leading edge of sail luff areillustrated.

Drawing 004

fig n—is the enlarged isometric view of said sprit.

fig o—is the enlarged top view of said sprit.

fig p—is the enlarged side view of said sprit

fig q—is an exploded view of said sprit itemizing each part number

List of Parts describes part names as indicated in fig q.

1. The assembled bowsprit forms a structurally rigid triangle. Itconsists from two equal lengths tubes joined together at one end withhead, forming “V”. The open ends are tied together with a tube. Thistube is also a hinge along which bowsprit rotates up or down.
 2. Thehinge assembly consists from the above mentioned tube and sleeve withbushings. The sleeve is a tube bonded through the hull in a horizontalposition, perpendicular to longitude axis with the ends protruding fromthe hull sides. The sleeve to hull joint shall be water tight,preventing water leaking to the boat.
 3. Bobstay's main function istransferring forces generated by sail and head stay to the boat. Unlikea fixed bowsprit with a fixed length permanent bobstay, the length ofthe folding bowsprit bobstay is easily adjustable. The bobstay lengthadjustment allows bowsprit to rotate up or down which is main featureand improvement of the folding bowsprit. The bobstay end is attached tobowsprit head and then led at approximate 45° angle to a pulley attachedto boats stem and up to deck level where it is secured at desiredlength. By loosening up the bobstay, the bowsprit end can rotate up andby tightening the bobstay (shorter length) the bowsprit end is pulleddown.
 4. If desired the bobstay tension could be finely adjusted underthe load, this could be used for example on racing sailboats where everyadjustment can improve boats performance. A good example of theadjustable length bobstay is a similar system used for a sailboat angleboom control called boom yang.